Known commercially available plant protective covers comprise transparent or opaque thermoplastic flexible films or rigid sheets used for covering plants to protect them from environmental factors such as extreme temperatures, harmful insects, dust, infrared (IR) radiation and ultraviolet (UV) radiation.
For example, U.S. Pat. No. 4,895,904 discloses polymer sheets or films for use in the construction of greenhouses. The polymer sheets or films contain additives, which absorb or reflect light in the near IR region, as well as additives for the stabilisation of UV radiation. These sheets are essentially transparent to the photosynthetic active region of the light spectrum.
Further for example, JP 7067 479 discloses a material for enhancing plant growth by manipulating the transmitted light spectrum. The material incorporates additives for screening IR, transmitting visible light and only partially transmitting UV.
Other known plant covers are sold under the Smartlight™ and Sun Selector™ trade marks. Photosynthesis strongly depends on the total amount of light that plants receive in the photosynthetic active region with major contributions from blue and red light. The Smartlight™ cover is a photo-selective plant cover that converts part of the UV light to red light, whilst also limiting the transmission of light on the longer end of the wavelength spectrum.
The Sun Selector™ film is a multi-layer photo selective film for use in the construction of greenhouses and tunnel coverings. The Sun Selector™ film contains IR additives to enable the film to absorb or reflect IR radiation. This film is further stabilised against UV radiation. Maximum light is transmitted in the visible range between 400 nm and 700 nm.
The known plant protective covers are primarily aimed at protecting a plant, cultivated underneath the cover, from environmental variables. These covers allow non-selective maximum transmission in the visible light range of the spectrum (400 nm-750 nm). However, they do not provide optimal transmittance spectra in the photosynthetic active region or cater for the specific photosynthetic and photomorphogenic needs of different varieties of plants. This is a disadvantage since different plant varieties respond to different photosynthetic and photomorphogenically active wavelengths of light and the known plant covers do not discriminate selectively between the said different wavelengths nor do they provide optimal transmittance spectra, which favours most plant varieties. The positive effect of the prior art covers on plants is therefore limited.